A distant observer, observing from far away but in the plane of the Solar System tries to measure the orbital speed of Mercury.
a. How much is light from Mercury redshifted or blueshifted as it orbits the Sun? Express your answer in ??/?.
b. If the measurements are made in visible light at ~5000Å, by how much is a spectral line shifted? Give your answer in Å.
c. If your spectrograph is capable of measuring shifts as small as 0.01Å, can it make the measurement?